Null and domain-activating mutations of the basement membrane laminin alpha2 (merosin) subunit are reported to cause human and murine congenital muscular dystrophies and peripheral nerve defects. Our laboratory is studying the inductive role of laminins on myotubes and Schwann cells, and preliminary data reveal that alpha2-laminin and its alpha1-laminin homologue binding to myotube cell surfaces through laminin G protein-specific integrin and alpha-dystroglycan receptors. These cruciform laminins self-assemble into polymers through their short arms, cluster the two receptors into polygonal complexes through their anchored long arm, and induce the formation of a vinculin-rich cortical cytoskeletal lattice that mirrors the organization of laminin and its receptors. We also have evidence that alpha2-laminin bearing the dy/2.1 dystrophic deletion is defective in its ability to self-assemble, to aggregate its receptors, and to assemble this cortical architecture. Based on these and other data, our working hypothesis is that laminin-2 plays a major role in driving the assembly of the myotube and Schwann cell cytoskeleton, a process mediated by its ability to bind to the cell surface, to polymerize, and to activate and reorganize its cognate receptors. This receptor and cytoskeleton reorganization, resulting from a dynamic integration of laminin activities, may be important for the development, maintenance and stabilization of muscle and nerve sheaths. Furthermore, a loss of one or more of these functions may cause muscular dystrophies with neuropathies. We propose to explore this concept in the following specific aims: I. Laminin-Myotube and Laminin-Schwann Cell interactions: We will study the composition, architecture, and sequential assembly of laminin-induced receptor-cytoskeletal complexes in normal and receptor-deficient myotubes and Schwann cells. II. Structure and function of Recombinant alpha2-Laminins Bearing Dystrophic Mutations: We will prepare and evaluate the structure and function of recombinant laminins bearing dystrophic alpha2-subunit mutations with respect to their structure, domain stability, self-assembly, and receptor activities. III. Dystrophic Recombinant Laminin Induction of Receptor-Cytoskeletal Complexes: We plan to study engineered laminins with respect to their ability to induce membrane cytoskeletal networks in myotubes and Schwann cells.